Electronic transmission of information to each of a plurality of users or subscribers of an information providing service is now common, as exemplified by satellite and cable system delivery of television and audio information. FIG. 1 is a simplified block diagram of a satellite system 10 for delivering information to multiple subscribers or users located over a large area. In FIG. 1, a ground station 12 with at least an uplink antenna 14 provides streams of information to a receiving or uplink antenna 22 of a spacecraft 20. The spacecraft 20 may be in a geosynchronous orbit, which remains at an apparently fixed location in the sky, as seen from a plurality of users 1, 2, . . . , N. Users 1, 2, . . . , N are located in a coverage area 26 of the beam, illustrated as 25, of a spacecraft transmitting or downlink antenna 24. A ground station, which may be ground station 12 or another ground station, also provides control functions for maintaining the spacecraft 20 in proper orbit and operating condition.
The streams of uplink information transmitted by ground station 12 of FIG. 1 and its antenna 14 to uplink antenna 22 of spacecraft 20 may be somewhat processed in the spacecraft 20, but the spacecraft and its antennas can often be viewed as being simply a “bent pipe” which retransmits the uplinked information streams along a downlink path by way of downlink beam 25. The uplink and downlink operating frequencies often differ, for reasons related to the gain of user receiving antennas relative to those of a ground station, and possibly also because of the relative efficiencies of electronic components at the different uplink and downlink frequencies.
Ideally, spacecraft 20 would include a “transponder” which would receive all the uplinked signals, amplify them, and retransmit the amplified signal along downlink beam 25 to the users. However, because of limitations on the undistorted power available from available transponders, many transponders are used, each operating at a somewhat different frequency within the available uplink/downlink frequency band. In one current application, the spacecraft includes thirty-two transponders or physical channels, each of which handles multiple separate programs. A program may include several primary streams of data, such as audio and video and security data.
In the abovementioned current application, the signal streams are in digital form, and the primary program streams are time-division multiplexed (TDM) within the channel defined by the transponder. Those skilled in the art know that such time division multiplexing requires advanced controls for assigning the information packets of the various independent signal channels to the signal path without overlap of the packets. The downlink signals arriving at the user terminals 1, 2, . . . , N of FIG. 1 by way of antenna beam 25 are so encoded. In addition, the information content sent over the satellite communication system may be “scrambled” or encoded in some additional way, not related to the mode of delivery over the spacecraft, to thereby prevent use of the content by persons not entitled to the content by virtue of having paid for access. In this manner, an appropriately programmed smartcard or security module is needed in order to receive the downlinked information. For example, all subscribers to the satellite system may have access to certain channels, and for this purpose they require at least the slot encoding information. While access to the encoding information may make it possible for a user to correctly receive the transmitted information on a premium channel, that transmitted information may be subject to an additional layer of encoding for which the non-paying subscriber does not have the key. Thus, a multiple-tier system is provided.
The operator of the satellite information video (and associated audio) delivery system controls the use of the delivered information stream by the use of Entitlement Control Messages (ECM) and Entitlement Management Messages (EMM). Entitlement Control Messages allow conditional access to the keys for decrypting the video stream of interest, and are delivered to the user as an integrated part of the video program, which is to say within the same physical channel as the program content. In the case of ordinary broadcast video, the physical channel is 6 MHz “wide.” In the case of a cable television system, the Entitlement Control Message may be delivered on a separate, dedicated “out-of-band” channel requiring a separate or secondary tuner. This may be done so that a user can receive security information while simultaneously viewing a traditional analog television signal in which there is no mechanism for the transmission of security information.
Typically, ECMs contain the keys necessary to descramble the program in addition to a description of the tier of subscription required to access the program. The ECMs are delivered as an MPEG transport packet, possibly every 10 milliseconds, and change periodically, possibly every 30 seconds. The ECMs are identified by the program ID number (PID) of the packet. This information is typically available through the system program guide or program map information. As a user tunes a desired channel, the receiver queries the guide information to find the PID associated with the ECM to gain access to the audio/visual streams. The receiver then finds the ECM packets related to the desired programming and passes these packets to a smart card or security module for processing. The security module opens the packets and compares the access rights of the program with the subscription level of the receiver. If the subscription level of the receiver is sufficient to permit viewing of the program, the security module decodes the decryption key and makes it available for descrambling of the program content. For those programs which exceed the current subscription level of the receiver, those keys are not made available and the receiver will not be able to descramble the content.
Entitlement Management Messages (EMM) are encrypted packets that allow for managing the rights of the receiving users to receive or not receive program content or data. EMMs are ordinarily sent to the user with a lower priority or lesser urgency than the Entitlement Control Messages (ECMs). The EMMs can be delivered in the same physical channel or in other physical channels, so long as the receiver knows a priori where and when to find them. In receivers with limited tuners, EMMs are typically transmitted simultaneously on all the physical channels to ensure that the receiver can always receive the EMM information regardless of the channel to which the receiver is currently tuned. EMMS are delivered as part of an MPEG transport stream and identified with a specific PID in a manner similar to that of the ECMs. An electronic address that can be associated with one or more receivers is typically found within the EMM packet. Typically, the receiver will look at all ECM packets delivered by the network and compare the receiver electronic address with the electronic address delivered in the EMM. If the addresses match, the EMM message is intended for the receiver, and the receiver will act in accordance with the information delivered by the EMM.
FIG. 2a is a simplified block diagram of processing which is performed at the head end or a ground station of a system for transmitting audio/video material to subscribers by way of a satellite. In FIG. 2a, a set 250 including a plurality of signal processors 251, 252, 250N each receives one of a plurality of input signal streams. In one embodiment, eight channels of audio-video (AV) information are applied to each processor of set 250. Each processor processes its own set of input AV information, and produces MPEG-encoded, time-division multiplexed, channelized radio-frequency information at its output terminal, for application by way of a combining (comb) arrangement illustrated as 260 to antenna 14 of FIG. 1.
FIG. 2b is a simplified block diagram of the processing 252 which is performed for one physical channel of FIG. 2a. It should be understood that a channel in the arrangement of FIG. 2b corresponds to a spacecraft transponder channel, because of the need to limit the number of signals traversing each spacecraft transponder channel. For definiteness, FIG. 2b represents physical channel 252 of FIG. 2a. In FIG. 2b, a plurality of audio/video sources or signal streams, which in one embodiment includes eight AV streams, are applied to the system. The eight audio/video streams of FIG. 2b are designated “transponder channel II,” thereby representing by a roman numeral that these signals are related to the “second” spacecraft transponder channel. The eight AV streams are applied over a plurality of signal paths 210a, 210b, . . . , 210N to a corresponding plurality of MPEG encoders 212a, 212b, . . . , 212N. MPEG encoding is advantageous for limiting or controlling the bandwidth of each video stream. Other compression techniques could also be used. It should be understood that some content channels may contain information other than video, which may require other encoding. The MPEG-encoded signals are transmitted from encoders 212a, 212b, . . . , 212N by way of paths 214a, 214b, . . . , 214N, respectively, to a transport multiplexer (MPX) 216. In addition to the MPEG-encoded content, the MPEG-encoded Transport multiplexer also receives user guide information over a path 217 from a block 218 and dummy EMM/ECM information over a path 219 from a block 220. The dummy EMM/ECM information is merely a “place holder” in the multiplexed data stream for the actual EMM/ECM information which will be transmitted. Transport multiplexer 216 combines the input information onto a single path 224. In one version of the prior art, the multiplexing is performed in a time-division-multiplex (TDM) manner, in which the information to be transmitted is broken into “packets,” which are then interleaved in time. The multiplexed information from multiplexer 216 is applied over a path 224 to an encryption apparatus illustrated as a block 230. Encryption block 230 encrypts the multiplexed data stream using a key provided over a path 233 by a key generator 232.
Encryption apparatus 230 of FIG. 2b also substitutes the key and access information into the space occupied in the incoming data stream by the dummy EMM/ECM bits. This step is illustrated in FIG. 2c, in which the stream of dummy ECM information currently traversing the encryptor is illustrated as 290. In FIG. 2c, the ECM information is inserted into the blank or dummy ECM. The ECM information contains the keys associated with a single program and information regarding the purchase rights necessary for a receiver to gain access to the keys. This ECM packet may be further encrypted with a high level system key to limit access. In FIG. 2c, the entire content K1 is illustrated as being decomposed into smaller sub-units K1a, K1b, K1c, . . . , K1X, representing all the information and keys associated with program 1. The resulting stream of encrypted TDM-multiplexed information produced by encryption block 230 of FIG. 2b, with its EMM/ECM information, is sent over a path 239 to a conventional transmitter, illustrated as a Modulator and Power Amp block 240. Transmitter block 240 modulates the signal onto one or more carriers, and raises the power of the signal. The resulting modulated, high power signal is sent from transmitter block 240 of FIG. 2b to combiner 260 of FIG. 2a for combination with other streams of modulated, high power signals and for application of the combined signals to antenna 14 of FIG. 1 for transmission to the spacecraft 20. The carrier frequency (frequencies) onto which the signals are modulated by each processor of set 250 of FIG. 2a is often selected in conjunction with the capabilities of the spacecraft to aid in separation of the modulated carriers into the available transponder channels of the spacecraft.
At the spacecraft 20 of FIG. 1, the uplinked groupings of channels are frequency-converted and amplified for retransmission to Earth. FIG. 3 is a simplified block diagram of the processing at the spacecraft. In FIG. 3, receiving or uplink antenna 22 receives the uplinked encoded TDM signals and couples the signals to a frequency separation filter 310, which routes the signals, according to their frequencies, by way of a plurality of signal paths designated 312a, 312b, . . . , 312N to a like plurality of transponders 301, 302, . . . , 300N. Each transponder illustrated in FIG. 3 includes a low-noise amplifier (LNA) for amplifying the received signals to compensate for path and other losses. It should be understood that the LNA could precede, rather than follow, the frequency separation filter 310. Each transponder 301, 302, . . . , 300N also includes a frequency converter, for converting the uplink frequency of each group of channels to a different frequency for transmission over a downlink to the users on Earth. The downlink frequencies are different among the groups of channels, for easy frequency separation. Each transponder of FIG. 3 also includes a power amplifier, for amplifying the frequency-converted signals in the transponder channel, to aid in overcoming losses in the downlink signal path to the user. The frequency-converted, amplified signals produced at the output of each channel 301, 302, . . . , 300N are applied to a combining arrangement, which may be a frequency-sensitive combiner, for forming a combined downlink signal for application to the downlink antenna 24 of FIG. 1.
FIG. 4 illustrates an arrangement 426 which might be found at a user, such as at user 2 of set 26 of users of FIG. 1. In FIG. 4, the user 2 includes an antenna 414 directed toward the spacecraft 20 of FIG. 1, for receiving the downlink signal, possibly including 32 transponder channels, each carrying the time-division information from eight audio/video channels together with EMM/ECM information. A receiver illustrated as a block 410 in FIG. 4 selects for reception one of the 32 downlinked channels, and produces on a signal path illustrated as 412 the stream of corresponding data. A transport demultiplexer or demultiplexor (deMux) block 416 receives the time-division multiplexed data stream and the encryption codes. The ECM information is provided to a smartcard or security module illustrated as 417 that compares the codes with the authorizations of the local user, and if authorized, provides keys for the transport demultiplexer 416 to descramble, decompress, and process the program for viewing on a television receiver 418 according to the selected audio/visual channel.
FIG. 7a illustrates the general tenor of the key distribution in the prior-art arrangement illustrated with reference to FIGS. 1, 2a, 2b, 2c, 3, and 4. As illustrated in FIG. 7a, each of the encryption blocks 216a, 216b, . 216N of the various processors 251, 252, . . . , 250N, respectively, of each of the physical channels, receives, over a path 233, keys produced by key generator 232. Each of the encryption blocks receives the keys for programs carried over the physical channel associated with the processor, and encodes the keys in the form of ECMs for the physical channel onto the signals traversing its own physical channel.
Non-legitimate access to the content of a system such as that set forth above in conjunction with FIGS. 1, 2a, 2b, 3, and 4 can be gained by compromising either the ECM or the EMM streams distributed to a receiver. In the case of ECM, a hacker would likely enable the viewing of a particular program or program segment, while in the case of the EMM, the hacker would potentially generate access to all encrypted materials on the network for an indefinite period of time. The hacker needs only to access the single physical channel in which the ECM or EMM information is delivered, and store the information for analysis and information extraction. This can be accomplished in the arrangement of FIG. 4 by the use of a computer illustrated as a block 420 connected to receive the audio/video data stream and the EMM/ECM data on signal path 412. The analysis can be done off-line once the information is stored. Once the hacker has succeeded in breaking the ECM, he can access all programming which uses the same ECM, and if the EMM can be determined, he can access all materials.
Improved or alternative information delivery systems are desired.